Separate application of liquid resin and hardener components in the form of strands by means of an application device comprising two independently mounted application heads, each comprising a hollow member, such as a tube, having a row of orifices through which the resin and hardener components are separately spread after each other onto the substrate, is known e.g. from SE 373 525.
A process like the one described in SE 373 525 is used for production of different laminated wood based products such as laminated wood, laminated timber, glued-laminated wood, glulam, I-beam, KVH-beam, Duo- and Trio-beams.
Melamine-urea-formaldehyde (MUF), melamine-formaldehyde (MF) or phenol-resorcinol-formaldehyde (PRF) glue systems are the most used systems for production of the above mentioned laminated products.
During the application of glue and hardener, the substrate to be glued is moved under the application heads, normally by means of conveyors or the like. Surplus glue and hardener is recovered in trays under each application head and is recirculated by means of pumps and piping to the respective application head. The liquid hardener or glue is preferably filtered either by means of a filter in the trays or in separate filtration units.
A problem with the kind of device described in SE 373 525 is that the hardener and/or glue dries and stops the orifices in the application heads during a short or long stop in the production. The application heads therefore have to be dismounted from the device and cleaned to remove remaining glue or hardener from the application heads for longer scheduled or not scheduled stops. The maximum allowed stand still time without having to wash the heads to avoid that the orifices are stopped may vary from hardener to hardener or from one glue to another.
Washing of the application heads is undesirable as it is an extra working operation adding cost to the gluing process. Resin and hardener may include products that require special provisions to avoid an unacceptable working environment. The components of the glue system and/or detergents do also normally include environmental harmful ingridiences. Accordingly, the remains from the washing and washing water have to be handled as a special waste and be deposited. This special handling and extra processes adds complexity and cost to the application process.
Devices for avoiding drying out and/or stopping of nozzles are known from U.S. Pat. Nos. 4,416,213, 4,489,856 and JP 59069173.
According to U.S. Pat. No. 4,416,213 a cup filled with solvent vapor is fitted to the lower end of a nozzle when not in use in an apparatus for rotary coating, to avoid evaporation of solvent resulting in change of viscosity in the liquid in the nozzle.
U.S. Pat. No. 4,489,856 relates to a methods and apparatus where a nozzle for applying an air-curable adhesive normally is located in a storage position having the end of the nozzle inserted into a liquid in the sump, and where the nozzle is lifted out of the sump, the sump is moved and the nozzle is moved to a position for applying the adhesive.
JP 59069173 relates to a device for application of a self-hardenable viscous liquid to a surface, wherein the nozzle is immersed in a hardening inhibiting liquid when it is not in use.
The above-identified prior art all relates to single nozzles and devices for applying one component coating or glue. The references do not disclose or suggest methods or devices for application of glue by means of applicators having a plurality of nozzles or devices for application of gluing systems where a resin component and a hardener component are applied separately.